DUPONT, Wash. — An Amtrak train making its inaugural trip on a new service from Seattle to Portland, Ore., derailed near here early Monday while crossing an overpass, toppling cars onto one of the busiest highways on the West Coast, killing at least three people and injuring about 100.

The wreck left 65-ton passenger rail cars scattered — several of them on the highway below, one tucked under the bridge it was to cross, others beside the railroad embankment and one dangling from the bridge with an end resting on the rail car that had been in front of it. In all, 13 of the train’s cars jumped the tracks, officials said.

At least five vehicles passing below on Interstate 5 — including two tractor-trailers — were heavily damaged as the rail cars from Amtrak Cascades train 501 fell from above.

Seconds later a member of the train crew radioed a dispatcher: “Amtrak 501, emergency, emergency, emergency. We’re on the ground. . . . We were coming around the corner to take the bridge over I-5 there, right north in Nisqually, and we went on the ground.”

The dispatcher asked, “Is everybody okay?”

The crew member replied: “I’m still figuring that out. We got cars everywhere and down onto the highway.”

He was one of five crew members aboard the train, along with 80 passengers, Amtrak said.

A Washington State Police spokeswoman said three people had been confirmed dead and about 100 people were transported to hospitals, many of whom remain in critical condition. It was unclear whether everyone had been accounted for.

“There are a lot of critical injuries,” spokeswoman Brooke Bova said. “This is a very complex scene.”

Authorities said they do not know what caused the crash but speed appears to be a factor.

Late Monday, the National Transportation Safety Board, which had sent investigators to the scene, announced that agency officials found the event data recorder aboard the train. Preliminary data shows the train was traveling at 80 mph when it derailed, officials announced.

Trains are supposed to reduce their speed to 30 mph to negotiate the curve, according to Rachelle Cunningham, a spokeswoman at Sound Transit, which owns the tracks.

At a news conference at NTSB headquarters in Washington, D.C., earlier Monday, board member Bella Dinh-Zarr had few details about the crash.

Dinh-Zarr said the agency’s team of investigators would include at least a dozen specialists in train operations, mechanics, tracks, signal systems, human performance and survival factors. The lead investigator is Ted Turpin, who also worked on the 2015 Amtrak derailment in Philadelphia and was the lead investigator for the Long Island Rail Road train crash at New York’s Atlantic Terminal early this year.

She said NTSB investigators will also be assessing what crash-avoidance technology existed on the tracks or on the train and whether that technology functioned properly.

Though Amtrak trains are equipped with it, the railroad said the train was not using positive train control, a system that would have slowed it as it entered the curve. The system requires that sensors also be placed along the rail bed, and those were not scheduled to be in place until sometime next year, according to the Washington State Department of Transportation.

The Amtrak Cascades train has daily service between Seattle and Portland, departing from Seattle at 6 a.m. local time. DuPont is about 50 miles south of Seattle; the crash happened between the Tacoma and Olympia rail stops, shortly after 7:30 a.m.

Chris Karnes, a passenger, said the train was approaching a curve at a high speed before it came off the tracks.

“It seemed like we were reaching sort of a bend in the tracks and all of a sudden we were slammed into the seats in front of us,” Karnes told CBS News. “And then the car careened down an embankment and came to a stop. After that happened we could hear and feel the cars crumpling and breaking apart.”

Karnes, who was in a car toward the front of the train, said he and other passengers had to kick out a window to get out. Passengers had visible injuries — “cuts, people bleeding,” he said. “I did see one person who was laying on the ground and not moving.”

Daniel Konzelman was driving down the highway when he and a friend saw the jumble of derailed cars. The emergency response training he’d acquired during his Eagle Scout days kicked in, and Konzelman, 24, immediately pulled over, according to the Associated Press.

He and his friend climbed into train cars to look for victims. Some were pinned under the train; others appeared to be dead. Konzelman helped the passengers who looked as if they could move out of the train and tried to comfort those who looked seriously injured. He and his friend stayed for almost two hours. “I wasn’t scared. I knew what to expect,” Konzelman said, adding: “I prepared for the worst and hoped for the best. I saw a little bit of both.”

Danae Orlob, 27, of Olympia, was in the back seat of a car that passed under the bridge moments after the derailment occurred, before any authorities had arrived.

“What I originally thought was a semi was actually a train car just flattened on the ground,” said Orlob, who was on her way into work in Bellevue. “The train cars were on both sides of the bridge, which I can’t even imagine how that would have happened.”

She said there was a stillness in the moments after the crash, as if everyone was stunned. “It was quiet. It was weird, and made me think the accident had been there much longer than it had,” she said. “It was definitely surreal.”

She looked back and saw a single rail car dangling over the highway from the bridge.

“It looked mostly intact, so the best thing I could hope was, I hoped everybody could have gotten out of there okay,” she said.

Within a minute, she said, a police car pulled up to the scene. Then an avalanche of first responders, ambulances, firetrucks and other emergency vehicles poured onto the highway.

The Amtrak train was on its first run on tracks that had been rebuilt at a cost of $181 million, using a 14.5-mile bypass owned by the regional transit authority and avoiding a more scenic but slower passage along the coastline. Officials celebrated the opening of the Tacoma station along the rebuilt route with a ribbon cutting Friday.

The new Amtrak Cascades service is part of an expansion of Amtrak intercity passenger rail service that includes station upgrades and expansions and the addition of new locomotives.

An Amtrak train derailed Monday morning in Washington state about 40 miles south of Seattle. (Washington State Patrol)

Though the train had been tested on the track, Monday’s run was the first time it made the trip with a full load of about 80 passengers and their baggage.

Washington and Oregon jointly operate the Amtrak Cascades intercity passenger service. The trains share the tracks with freight trains and are authorized to travel at top speeds of 79 mph, according to information from the Washington State Department of Transportation.

The new service is said to save 10 minutes in travel time between Seattle to Portland.

“On behalf of everyone at Amtrak, we are deeply saddened by all that has happened today,” Amtrak president and co-chief executive Richard Anderson said in a statement Monday. “We will do everything in our power to support our passengers and crew and their families.”

At an afternoon news conference, Gay Banks Olson, assistant superintendent at Amtrak, said the railroad’s first priority is to take care of passengers, employees and relatives affected.

“It is horrible that this happened to these passengers, but we are very grateful that there weren’t more people involved,” Banks Olson said. “We are going to do everything we can in the next few days and weeks to support these passengers and their families.”

State police are providing resources and getting supplies to the scene, the spokeswoman said.

Gov. Jay Inslee (D) said on Twitter: “Today’s tragic incident in Pierce County is a serious and ongoing emergency. Trudi and I are holding in our hearts everyone on board, and are praying for the many injured.”

Rescue crews had to use chain saws, hydraulic equipment, air chisels and various other tools to extricate victims.

Jay Sumerland, battalion chief with West Pierce Fire and Rescue, described the scene as surreal.

“When there are cars dangling over the freeway, it’s very precarious and dangerous to the fire service crews,” he said. “Firefighters put themselves in a very dangerous place and did a great job searching all over those cars.”

The power car behind the locomotive carried 350 gallons of fuel. The Washington State Department of Ecology and Amtrak were working on mitigation. Washington State Patrol Chief John Batiste said his agency performed an initial investigation in anticipation of NTSB’s arrival.

Cranes also were being brought in to stabilize the cars before state transportation officials could inspect the bridge.

Lazo and Halsey reported from Washington, D.C. Martine Powers and Faiz Siddiqui in Washington, D.C., contributed to this report.